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Only true way to test a diode is take it out of the circuit and test, can have a max of ONE circuit connection to it remaining. I like using an analog meter, once you test a good diode you'll see the pattern of a good one. The resistance while conducting all seem to fall in same meter deflection position. https://www.smokstak.com/forum/attac...4&d=1344478607

But may times in other electronics you can still see that it's acting as a diode even though it's still in the circuit. Guessing with windings resistance of winding is so low you'll have to take it out of the circuit to test it

Once I verify that the diodes are good with an analog ohm meter, I always load them with about half their rated amperage with a lamp in both directions.

I've found many diodes over the years that check good with a meter, but break down under load. With gen end diodes, I usually use a halogen headlight bulb. Under load, I like to see no less than .7-1.0V max drop when comparing the voltage at the load to the voltage at the source.